The present invention is directed generally to a printing ribbon spool. More specifically, the present invention is directed to a printing ribbon spool of the type having a storage means for storing ink internally of the spool and a means for transferring ink from the storage means to the printing ribbon.
Printing ribbon spools of the aforementioned type are generally known. See, U.S. Pat. Nos. 3,819,026 and 4,115,012, incorporated herein by reference. These patents generally disclose a printing ribbon spool for maintaining the printout density or consistency of a printing ribbon by contact between a woven or knitted ink pad on the spool and a side edge of the ribbon. Ink is communicated to the pad from a hermetically sealed reservoir internally of the spool by way of woven or knitted wicks which communicate with the reservoir through wick holes substantially smaller in diameter than the transverse width of the wicks in their normal uncompressed condition.
A problem with the printing ribbon spools disclosed in the aforementioned patents is that they cannot be stored or shipped under adverse conditions, i.e., extreme conditions of temperature or heat. A drop in ambient pressure, such as would occur during shipment by air freight, causes the ink to bleed from the hermetically sealed reservoir to the ink pad. The ink in the reservoir is thus depleted even before the spool is used and shipment becomes messy because of the leaking ink. Storing or transporting the ribbon spool at elevated temperatures, such as may occur in the trunk of a car on a sunny day, results in the same bleeding action and creates the same undesirable conditions.
An additional problem with the printing ribbon spools described in the aforementioned patents is that they are limited in printing speed. It has been found that there is a direct relationship between the diameter of the wick holes and the speed at which the printing spool may operate without degredation or inconsistency in print-out density. That is, the faster the ribbon is unwound from the spool, the faster the ink needs to be conducted from the reservoir to the ink pad to maintain a consistent print-out density. Experimentation has shown that if the diameter of the wick holes of the '012 and '026 patent spools is made larger than 0.094", ink will bleed from the reservoir even in non-adverse storage conditions. This places a practical limitation on the size of the wick hole diameter that may be provided in those prior art spools. Thus, the speed at which prior art ribbon spools of the above-mentioned type can be driven is limited due to limitations in the maximum diameter of the wick holes.
Still a further problem with the printing ribbon spools described in the aforementioned patents is that the print-out density does change somewhat as the ink level in the reservoir decreases, even when operating at slower speeds. Initially, the ink level is equal to or above the level of the wick holes. The ink pressure causes the ink to be conducted to the pad at a greater rate than when the ink level drops below the level of the wick holes.
Still a further problem with prior art printing ribbon spools is that they have a limited shelf life. Although ink is stored in a hermetically sealed reservoir in the spool, the ink may bleed out of the reservoir over a period of time because the wick holes contact the ink even during storage.
These and other failings of the aforementioned prior art ribbon spools are overcome by the present invention.
Another kind of typewriter ribbon re-inking device is taught by U.S. Pat. No. 2,743,470. The '470 patent discloses a cylindrical casing having an ink scraper and an ink pad disposed therein. An ink storing chamber is also disposed in the casing above the ink pad and means are provided to allow the ink to pass from the chamber to the ink pad by means of a valve. A transverse slot for receiving the printing ribbon extends through the casing for re-inking the ribbon.
The '470's re-inking device is fraught with practical problems. The re-inking device must be either manually held over the ribbon or attached to the typewriter by a mechanical linkage. Additionally, the valve must be manually released for the purpose of replenishing the ink pad. Still further, the ink storage chamber is not hermetically sealed, and is not capable of being hermetically sealed without adversely affecting the device's operation. Moreover, the '470 patent's provision of an air hole from the chamber to the atmosphere does not permit a regulated flow of ink to the ink pad, i.e., ink may flow to the pad until it is saturated if the valve is maintained in the open position. Still further, when the valve is removed for purposes of reloading the chamber with ink, a quantity of ink will pass into the ink pad, possibly over-inking the pad before the chamber has been completely filled and the valve has been reinserted. Each opening of the valve allows air to enter the chamber, thus negating any possibility of maintaining a vacuum in the chamber.
Additional problems are associated with the use of the '470 patent's re-inking device. This device cannot be used in any but an upright position since ink would leak outside the chamber through the air hole provided in the chamber wall.
These and other failings of the '470 patent's re-inking device are overcome by the present invention.